CN105681243A - Frame timing synchronization method applied to broadband OFDM power line communication system - Google Patents

Abstract

The invention provides a frame timing synchronization method applied to a broadband OFDM power line communication system. According to the frame timing synchronization method, through the pilot structure of connected positive and negative OFDM symbols and three-step synchronous positioning with alternated cross-correlation and self-correlation, synchronous position is accurate and reliable, synchronization performance of system data frames is improved, and a reliable OFDM symbol windowing position is provided for subsequent data demodulation, thereby enhancing the overall performance of the system to a great extent, being able to determine frame synchronization position in a power line environment with large noise and strong interference, and providing guarantee for the subsequent signal processing.

Description

Be applied to the frame timing synchronized method of wideband OFDM electric line communication system

Technical field

The present invention relates to low-voltage power line communication technical field, particularly relate to one and be applied to broadbandThe frame timing synchronized method of OFDM electric line communication system.

Background technology

Power line communication (PowerLineCommunication) system refers to and is based upon power delivery networkOn network basis, realize between the each node of power line network and with other communication networks between the system of communicating by letter.Power line communication utilization has electric power networks, separately frame communication line, and power line extends in all direction, toolThere is the advantage of the low and broad covered area of communications cost. But power line not aims at data communication design,On power line, noise is large, interference is strong, load impedance changes acutely, exists serious frequency selectivity to declineFall, to electric line communication system, design has proposed very high requirement.

Because the impact of time delay expansion brings serious intersymbol interference (ISI) single-carrier system not meetThe requirement of power line communication, therefore adopts OFDM (OFDM) technology of multi-carrier transmissionBe applied to electric line communication system. OFDM technology adopts multi-carrier modulation, data is divided into someIndividual parallel data stream, then be modulated to and on mutually orthogonal subcarrier, carry out parallel transmission. OFDM technologyThere is the feature of good anti-frequency selective fading and anti-ISI, be applicable to very much power line communication.Although OFDM symbol has good anti-ISI ability, and the orthogonality of carrier wave is had to strict requirement.In low voltage power line communication channel, non-ideal factor can cause synchronism deviation, thereby causes data demodulates mistakeMistake, therefore carries out accurate synchronously particularly important to Frame. Conventional leading symbol by single orMultiple identical OFDM symbol compositions, structure is more single, and the frame timing that can adopt is sameOne step process is also more single, easily misses symbol and cause sync bit mistake while carrying out Frame synchronous.

Summary of the invention

(1) technical problem that will solve

In view of above-mentioned technical problem, the invention provides one, to be applied to wideband OFDM power line logicalThe frame timing synchronized method of communication system.

(2) technical scheme

According to a first aspect of the invention, provide a kind of wideband OFDM electricity of carrying out at transmitting terminalThe frame timing synchronized method of line of force communication system. This frame timing synchronized method comprises:

Step S101: carry out OFDM modulation generated data frame to sending data;

Step S102: before the Frame generating, insert targeting sequencing, generate signal frame, wherein, frontLead sequence by several OFDM symbol-SYNCP and at least one OFDM symbol-SYNCM groupBecome; And

Step S103: signal frame is carried out to digital-to-analogue conversion, generate analog signal and send into power line channel.

According to another aspect of the present invention, also provide a kind of broadband that is applied in receiving terminal executionThe frame timing synchronized method of OFDM electric line communication system. This frame timing synchronized method comprises:

Step S104: receive analog signal from power line channel, this analog signal is carried out to modulus and turnChange, be converted into the signal frame of digital signal form;

Wherein, to carry out digital-to-analogue conversion by Frame and the targeting sequencing that inserts its front raw for this analog signalBecome, Frame carries out OFDM modulation generation by sending data; Targeting sequencing is by several OFDMSymbol SYNCP and several OFDM symbols SYNCM composition;

Step S105, carries out auto-correlation computation to the signal frame after conversion, by autocorrelation value corr₁WithDefault first threshold T_xRelatively, when having a continuous N numerical value, autocorrelation value is greater than first threshold T_xTime,Think and signal frame detected, one that auto-correlation is started as original position S1, and records that this is initialPosition S1;

Step S106: the lead data of utilizing the local storage of receiving terminal taking original position S1 as starting point withThe signal frame receiving carries out computing cross-correlation and obtains array corr in an OFDM symbol₂, byArray corr₂Compute sign timing position S2; And

Step S107: according to Symbol Timing position S2 and default Second Threshold Tx₂, utilize and receiveThe auto-correlation of signal obtains frame timing, completes frame Timing Synchronization, wherein, and Second Threshold Tx₂Equal negativeFirst threshold T_x1。

(3) beneficial effect

Can find out from technique scheme, it is leading that the present invention is joined by positive and negative OFDM symbolStructure, and cross-correlation auto-correlation intert three steps synchronously locate, make sync bit accurately and reliably,Promote the net synchronization capability of system data frame, for subsequent demodulation data provide reliable OFDM symbolThe position of number windowing, thus the overall performance of system promoted to a great extent, can be large at noise, dryDisturb in strong power line environment and effectively determine frame synchronization position, for follow-up signal processing is given security.

Brief description of the drawings

Fig. 1 is that to be applied to the frame of wideband OFDM electric line communication system according to the embodiment of the present invention fixedTime synchronous method flow chart;

Fig. 2 is applied targeting signal data structure schematic diagram in frame timing synchronized method shown in Fig. 1.

Detailed description of the invention

The present invention is mainly the targeting signal inserting before based on Frame, while receiving data-signal, passes throughThereby auto-correlation or cross-correlation are determined Symbol Timing, frame timing and are reached the object of correct reception data-signal.

For making the object, technical solutions and advantages of the present invention clearer, below in conjunction with concrete realityExecute example, and with reference to accompanying drawing, the present invention is described in more detail.

In one exemplary embodiment of the present invention, provide one to be applied to wideband OFDM electricityThe frame timing synchronized method of line of force communication system. As shown in Figure 1, the present embodiment is applied to wideband OFDMThe frame timing synchronized method of electric line communication system comprises two parts, and wherein Part I is held at transmitting terminalOK, Part II carries out at receiving terminal.

Continue referring to Fig. 1, in Part I, at transmitting terminal: insert before transmitting terminal FrameTargeting sequencing, targeting sequencing is by several identical OFDM symbol: SYNCP and SYNCM groupBecome, as shown in Figure 2. Wherein, SYNCP and SYNCM have the more uniform feature of symbol energy.

Specifically,, in Part I, transmitting terminal is carried out following steps:

Step S101: first carry out OFDM modulation generated data frame to sending data;

Step S102: before the Frame generating, insert targeting sequencing, generate signal frame, wherein, frontLeading sequence is made up of several OFDM symbol SYNCP and an at least individual OFDM symbol SYNCM;

Wherein, wherein SYNCP is that CENELEC-A frequency range in G3-PLC standard agreement is leadingSymbol, SYNCP is multiplied by-1 and obtains SYNCM. The number of SYNCP is generally got 5～10, thisIn embodiment, get 8; The number of SYNCM is generally got 1～2, and the present embodiment is got 1.5, thisThe meaning of 1.5 at place is to get a whole SYNCM and half SYNCM;

Step S103: signal frame is carried out to D/A (digital-to-analog) conversion, generate analog signal and sendEnter power line channel.

Continue referring to Fig. 1, in Part II, at receiving terminal: to synchronous point three steps of FrameCarry out: the first step, the auto-correlation of receiving terminal utilization reception signal is searched leading, when autocorrelation value hasContinuous N (M is the numerical value setting in advance) is individual to be greater than and to think inspection after the threshold value Tx setting in advanceMeasure the rough starting point of data frame signal; Second step, on the rough starting point basis obtaining to received signalDetermine Symbol Timing with local targeting signal cross-correlation; The 3rd step, at definite on last stage symbolOn the basis of timing, utilize the auto-correlation that receives signal to determine frame timing.

Specifically,, in Part II, receiving terminal is carried out following steps:

Step S104: receive analog signal from power line channel, this analog signal is carried out to A/D(analog/digital) changed, and is converted into the signal frame of digital signal form;

Step S105, carries out auto-correlation computation to the signal frame after conversion, by autocorrelation value corr₁WithDefault first threshold T_xRelatively, when having a continuous N numerical value, autocorrelation value is greater than first threshold T_x1Time, to think and signal frame detected, one that auto-correlation is started as original position S1, and record shouldOriginal position S1;

In this step, adopt following formula to carry out auto-correlation computation:

${\mathrm{corr}}_1\left(n\right)=\frac{1}{N}\underset{i=0}{\overset{N-1}{\Σ}}{y}_r(n+i)y_r(n+i+N)$

Wherein, when N is transmitting terminal OFDM modulation, IFFT counts, y_r(n+i) represent after analog-to-digital conversionThe range value of n+i sampled point; y_r(n+i+N) represent that n+i+N after analog-to-digital conversion is adoptedThe range value of sampling point, corr₁(n) represent the auto-correlation result of n sampled point as starting point.

Wherein, the value of M generally, between 5～15, is got M=10 in the present embodiment; The first thresholdValue T_x1Value relevant with signal amplitude, in the present embodiment according to the following formula calculate:

$T_{x1}=0.9*\underset{i=1}{\overset{N}{\Σ}}{\mathrm{SYNCP}}_i^2.$

In the present embodiment, N gets 256, T_x1＝38。

Step S106: the lead data of utilizing the local storage of receiving terminal taking original position S1 as starting point withThe signal frame receiving carries out computing cross-correlation and obtains array corr in an OFDM symbol₂, byArray corr₂Compute sign timing position S2;

In this step, adopt following formula to carry out computing cross-correlation:

${\mathrm{corr}}_2\left(m\right)=\frac{1}{N}\underset{i=0}{\overset{N-1}{\Σ}}{y}_r(S1-n_{adv}+m+i)s_{syncp}\left(i\right)$

Wherein, s_syncp(i) be the amplitude of i sampled point of the targeting signal of local storage. n_advFor fromThe figure place that previous step sync bit is searched for forward. M=0,1 ..., N_stage2-1，N_stage2For the inspection of this stepSurvey sampling number, y_r(S1-n_adv+ m+i) represent the S1-n after analog-to-digital conversion_adv+ m+i sampled pointRange value.

In this step, Symbol Timing position is obtained by following formula:

$S2=(S1-n_{adv})+\underset{m}{max}\left\{{\mathrm{corr}}_2\left(m\right)\right\}$

Wherein, max is array corr₂Maximum.

Step S107: according to Symbol Timing position S2 and default Second Threshold Tx₂, utilize signalThe auto-correlation of frame obtains frame timing, completes frame Timing Synchronization.

In this step, adopt following formula to carry out auto-correlation computation:

${\mathrm{corr}}_3\left(m\right)=\frac{1}{N}\underset{i=0}{\overset{N-1}{\Σ}}{y}_r(S2+m\·N+i)y_r(S2+m\·N+N+i)$

Wherein, m=0,1 ..., N_stage3-1，N_stage3For the detection duration of this step.

If for certain m value, corr₃(m) be less than predefined Second Threshold Tx₂, SYNCMThe timing S of symbol_SYNCMFor:

S_SYNCM＝S2+(m+1)·N

The timing that obtains SYNCM symbol obtains frame timing, and frame Timing Synchronization finishes;

Wherein, Second Threshold Tx₂Equal negative first threshold T_x1。

Otherwise, if corr₃(m) be more than or equal to Second Threshold, return to step 105.

Step S108: after frame Timing Synchronization finishes, the targeting signal in Frame is removed;

Step S109: Frame is carried out to OFDM demodulation and obtain transmitting data.

So far, by reference to the accompanying drawings one embodiment of the invention be have been described in detail. More than foundationDescribe, those skilled in the art should be applied to wideband OFDM electric line communication system to the present inventionFrame timing synchronized method had clearly understanding.

It should be noted that, in accompanying drawing or description text, the implementation that does not illustrate or describe,Under being, form known to a person of ordinary skill in the art in technical field, is not elaborated. In addition,The above-mentioned definition to each step method is not limited in various concrete structures, the shape in embodiment, mentionedOr mode, those of ordinary skill in the art can change simply or replace it.

In addition, can provide herein the demonstration of the parameter that comprises particular value, but these parameters are without definite etc.In corresponding value, but can in acceptable error margin or design constraint, be similar to analog value. AndAnd, unless describe especially or the step that must sequentially occur, the order of above-mentioned steps there is no be limited toUpper listed, and can change or rearrange according to required design.

In sum, the present invention overcome low voltage power line communication channel noise large, disturb strong defect, canWith better specified data frame synchronization position, thereby accurately receive in severe low voltage power line communication channelData, improve systematic function, have good using value.

Above-described specific embodiment, carries out object of the present invention, technical scheme and beneficial effectFurther description, institute it should be understood that the foregoing is only specific embodiments of the invention and, be not limited to the present invention, within the spirit and principles in the present invention all, any repairing of doingProtection scope of the present invention changes, be equal to replacement, improvement etc., within all should be included in.

Claims (10)

1. be applied to a frame timing synchronized method for wideband OFDM electric line communication system, its spyLevy and be, carry out at transmitting terminal, comprising:

Step S101: carry out OFDM modulation generated data frame to sending data;

Step S102: before the Frame generating, insert targeting sequencing, generate signal frame, wherein, frontLead sequence by several OFDM symbol-SYNCP and at least one OFDM symbol-SYNCM groupBecome; And

Step S103: signal frame is carried out to digital-to-analogue conversion, generate analog signal and send into power line channel.

2. frame timing synchronized method according to claim 1, is characterized in that, described stepIn S102:

SYNCP is the CENELEC-A frequency range leading symbol in G3-PLC standard agreement, SYNCPBe multiplied by-1 and obtain SYNCM;

The number of described SYNCP is got 5～10, and the number of described SYNCM is got 1～2.

3. frame timing synchronized method according to claim 1, is characterized in that, described SYNCPNumber get 8, the number of described SYNCM is got 1.5.

4. be applied to a frame timing synchronized method for wideband OFDM electric line communication system, its spyLevy and be, carry out at receiving terminal, comprising:

Step S104: receive analog signal from power line channel, this analog signal is carried out to modulus and turnChange, be converted into the signal frame of digital signal form;

Wherein, to carry out digital-to-analogue conversion by Frame and the targeting sequencing that inserts its front raw for this analog signalBecome, Frame carries out OFDM modulation generation by sending data; Targeting sequencing is by several OFDMSymbol SYNCP and several OFDM symbols SYNCM composition;

Step S105, carries out auto-correlation computation to the signal frame after conversion, by autocorrelation value corr₁WithDefault first threshold T_xRelatively, when having a continuous N numerical value, autocorrelation value is greater than first threshold T_x1Time, to think and signal frame detected, one that auto-correlation is started as original position S1, and record shouldOriginal position S1;

Step S106: the lead data of utilizing the local storage of receiving terminal taking original position S1 as starting point withThe signal frame receiving carries out computing cross-correlation and obtains array corr in an OFDM symbol₂, byArray corr₂Compute sign timing position S2; And

Step S107: according to Symbol Timing position S2 and default Second Threshold Tx₂, utilize and receiveThe auto-correlation of signal obtains frame timing, completes frame Timing Synchronization, wherein, and Second Threshold Tx₂Equal negativeFirst threshold T_x1。

5. frame timing synchronized method according to claim 4, is characterized in that, described stepIn S105, adopt following formula to carry out auto-correlation computation:

${\mathrm{corr}}_1\left(n\right)=\frac{1}{N}\underset{i=0}{\overset{N-1}{\Σ}}{y}_r(n+i)y_r(n+i+N)$

Wherein, when N is transmitting terminal OFDM modulation, IFFT counts, y_r(n+i) represent after analog-to-digital conversionThe range value of n+i sampled point; y_r(n+i+N) represent that n+i+N after analog-to-digital conversion is adoptedThe range value of sampling point, corr₁(n) represent the auto-correlation result of n sampled point as starting point.

6. frame timing synchronized method according to claim 5, is characterized in that, described stepIn S105, the value of M between 5～15, first threshold T_x1Calculate by following formula:

$T_{x1}=0.9*\underset{i=1}{\overset{N}{\Σ}}{\mathrm{SYNCP}}_i^2.$

7. frame timing synchronized method according to claim 4, is characterized in that, described stepIn S106, adopt following formula to carry out auto-correlation computation:

${\mathrm{corr}}_2\left(m\right)=\frac{1}{N}\underset{i=0}{\overset{N-1}{\Σ}}{y}_r(S1-n_{adv}+m+i)s_{syncp}\left(i\right)$

Wherein, s_syncp(i) be the amplitude of i sampled point of the targeting signal of local storage. n_advFor fromThe figure place that previous step sync bit is searched for forward. M=0,1 ..., N_stage2-1，N_stage2For the inspection of this stepSurvey duration, y_r(S1-n_adv+ m+i) represent the S1-n after analog-to-digital conversion_advThe amplitude of+m+i sampled pointValue.

8. frame timing synchronized method according to claim 4, is characterized in that, described stepIn S106, adopt following formula compute sign timing position S2:

$S2=(S1-n_{\mathrm{adv}})+\underset{m}{\max }\left\{{\mathrm{corr}}_2\left(m\right)\right\}$

Wherein, max is array corr₂Maximum.

9. frame timing synchronized method according to claim 4, is characterized in that, described stepIn S107, adopt following formula to carry out auto-correlation computation:

${\mathrm{corr}}_3\left(m\right)=\frac{1}{N}\underset{i=0}{\overset{N-1}{\Σ}}{y}_r(S2+m\·N+i)y_r(S2+m\·N+N+i)$

Wherein, m=0,1 ..., N_stage3-1，N_stage3For the detection duration of this step;

For certain m value, corr₃(m) be less than predefined Second Threshold Tx₂, SYNCM symbolNumber timing S_SYNCMFor: S_SYNCM=S2+ (m+1) N, otherwise, re-execute step S105.

10. according to the frame timing synchronized method described in any one in claim 4 to 9, its feature existsIn, in described step S104:

SYNCP is the CENELEC-A frequency range leading symbol in G3-PLC standard agreement, SYNCPBe multiplied by-1 and obtain SYNCM;

The number of described SYNCP is got 5～10, and the number of described SYNCM is got 1～2.